Numerous different types of volumetric feeding apparatus and methods are known in the material handling arts. Not all the known volumetric feeding apparatus and methods are suitable, however, for processing finely divided materials which flow freely when aerated or fluidized but which tend to agglomerate or cake when subjected to long term settling or vibration. Examples of such materials include powdered coal, flour, cement, fly ash, and the like.
Further, the known types of volumetric feeding apparatus and methods are not suited to injecting the measured granular material into a pressurized process stream without requiring auxiliary equipment such as an air lock and supplementary dust collecting means to assure dust-free operation.
Also, some types of volumetric measuring and feeding apparatus such as vibratory screw feeders suitable for feeding caking-type particulate materials are comparably more costly to construct.
We have discovered that an improved volumetric measuring and feeding apparatus may be constructed in a less costly manner and also operated to provide increased repeatability or accuracy of measurement for caking-type particulate materials to be fed into a pressurized process zone. The invention avoids the necessity of providing separate air lock equipment and associated dust collecting equipment.